Pressure compensating hydraulic control valve system

Abstract

An improved pressure-compensated hydraulic system for feeding hydraulic fluid to one or more hydraulic actuators. A remotely located, variable displacement pump provides an output pressure equal to input pressure plus a constant margin. A pressure compensation systems requires that a load-dependent pressure be provided to the pump input through a load sense circuit. A reciprocally spooled, multi-ported isolator transmits the load-dependent pressure to the pump input but prevents fluid in the load sense circuit from leaving the load sense circuit and flowing through a relatively long conduit leading to the remotely located pump. In a multi-valve array, at least one valve section has a backflow-preventing shuttle valve which prevents backflow through the pressure compensation system if a main relief valve is operative.

I claim: 
     
       1. In a hydraulic system having an array of valve sections for controlling flow of hydraulic fluid from a pump to a plurality of hydraulic actuators, each valve section having a workport to which one of the plurality of hydraulic actuators connects, the pump being of the type which produces an output pressure that is a constant amount greater than a pressure at a control input, the array of valve sections being of the type in which the greatest pressure among the workports is sensed to provide a load sense pressure which is transmitted to the control input; the improvement comprising: within each valve section, a pressure compensating valve that provides the load sense pressure at one side of a metering orifice which sees on the other side the output pressure of the pump so that the pressure drop across the metering orifice is substantially equal to the constant amount, the pressure compensator having a poppet slidably located in a bore thereby defining first and second chambers of the bore, the first chamber being in communication with the metering orifice and the second chamber being in communication with the load sense pressure wherein a pressure differential between the first and second chambers determines a position of the poppet with in the bore, the bore having an output port through which fluid is supplied to one of the hydraulic actuators, the poppet having a passage through which fluid can flow between the metering orifice and the output port when the poppet is at a first position in response to pressure in the first chamber being greater than pressure in the second chamber; and   a check valve within the poppet and controlling communication of pressure between the first chamber and one of the output port and the second chamber.   
     
     
       2. The hydraulic system as recited in claim 1 further comprising a pressure relief valve to which the greatest pressure among the workports is transmitted wherein the pressure at a control input is equal to the lower of (a) a set point pressure of the pressure relief valve and (b) the greatest pressure among the workports. 
     
     
       3. The hydraulic system as recited in claim 1 further comprising a spring located in the first chamber and biasing the poppet toward the first position. 
     
     
       4. A hydraulic valve mechanism for enabling an operator to control the flow of pressurized fluid in a fluid path from a variable displacement hydraulic pump to a hydraulic actuator which is subjected to a load force that creates a load pressure, the pump having a control input and producing an output pressure which is a constant amount greater than a pump input pressure, the hydraulic valve mechanism comprising: (a) a first valve element and a second valve element juxtaposed to provide between them a metering orifice in the fluid path, at least one of the valve elements being movable under the control of the operator to vary the size of the metering office and thereby to control the flow of fluid to the hydraulic actuator;   (b) a sensor for sensing the load pressure at the hydraulic actuator and applying the load pressure to the control input of the pump;   (c) pressure compensator for maintaining across the metering orifice a pressure drop substantially equal to the constant amount, the pressure compensator having a poppet slidably located in a bore thereby defining first and second chambers of the bore on opposing sides of the poppet, the first chamber in being communication with the metering orifice and the second chamber being in communication with the load pressure sensed by the sensor wherein pressure differential between the first and second chambers determines a position of the poppet with in the bore, the bore having an output port through which fluid is supplied to the actuator, the poppet having a passage through which fluid can flow between the metering orifice and the output port when the poppet is at a first position in response to pressure in the first chamber being greater than pressure in the second chamber; and   a check valve within the passage through the poppet and closing the passage in response to pressure at the output port being greater than pressure in the first chamber.   
     
     
       5. The hydraulic system as recited in claim 4 further comprising a spring located in the first chamber and biasing the poppet toward the first position. 
     
     
       6. A hydraulic valve mechanism for enabling an operator to control the flow of pressurized fluid in a fluid path from a variable displacement hydraulic pump to an hydraulic actuator subject to a load force which creates a load pressure, the pump having a control input and producing an output pressure which is a constant amount greater than the pump input pressure, the hydraulic valve mechanism comprising: (a) a first valve element and a second valve element juxtaposed to provide between them a metering orifice in the fluid path, at least one of the valve elements being movable under the control of the operator to vary the size of the metering office and thereby to control the flow of fluid to the hydraulic actuator;   (b) a transfer passage for communicating the load pressure to the control input of the pump;   (c) pressure compensator for maintaining across the metering orifice a pressure drop substantially equal to the constant amount, the pressure compensator having a poppet slidably located in a bore thereby defining first and second chambers of the bore, the first chamber being in communication with the metering orifice and the second chamber being in communication with the transfer passage wherein pressure differential between the first and second chambers determines a position of the poppet with in the bore, the bore having an output port through which fluid is supplied to the actuator, the poppet having a passage through which fluid can flow between the metering orifice and the output port when the poppet is at a first position in response to pressure in the first chamber being greater than pressure in the second chamber, said poppet having a pilot passage between the first and second chambers; and   a check valve within the pilot passage of the poppet and closing the pilot passage in response to pressure in the second chamber being greater than pressure in the first chamber.   
     
     
       7. The hydraulic system as recited in claim 6 further comprising a spring located in the first chamber and biasing the poppet toward the first position. 
     
     
       8. In a hydraulic system having an array of valve sections for controlling flow of hydraulic fluid from a pump to a plurality of hydraulic actuators, each valve section having a workport to which one of the plurality of hydraulic actuators connects, the pump being of the type which produces an output pressure that is a constant amount greater than a pressure at a control input, the array of valve sections being of the type in which the greatest pressure among the workports is sensed to provide a load sense pressure which is transmitted to the control input; the improvement within each valve section comprising: a pressure compensating valve that provides the load sense pressure at one side of a metering orifice which sees on the other side the output pressure of the pump so that the pressure drop across the metering orifice is substantially equal to the constant amount, the pressure compensator having a poppet slidably located in a bore thereby defining first and second chambers of the bore, the first chamber being in communication with the metering orifice and the second chamber being in communication with the load sense pressure wherein a pressure differential between the first and second chambers determines a position of the poppet with in the bore, the bore having an output port through which fluid is supplied to one of the hydraulic actuators, the poppet having a passage through which fluid can flow between the metering orifice and the output port when the poppet is at a first position in response to pressure in the first chamber being greater than pressure in the second chamber; and   a check valve within the passage of the poppet and closing the passage in response to pressure at the output port being greater than pressure in the first chamber.   
     
     
       9. The hydraulic system as recited in claim 8 further comprising a spring located in the first chamber and biasing the poppet toward the first position. 
     
     
       10. The hydraulic system as recited in claim 8 further comprising a chain of shuttle valves for selecting the greatest pressure among the workports of the hydraulic system. 
     
     
       11. The hydraulic system as recited in claim 8 wherein each valve section further comprises a shuttle valve having an output, a first input connected to the first chamber, and a second input connected the output of a shuttle valve in a different valve section of the hydraulic system. 
     
     
       12. The hydraulic system as recited in claim 8 further comprising a pressure relief valve to which the greatest pressure among the workports also is transmitted wherein the pressure at a control input is equal to the lower of (a) a set point pressure of the pressure relief valve and (b) the greatest workport pressure. 
     
     
       13. In a hydraulic system having an array of valve sections for controlling flow of hydraulic fluid from a pump to a plurality of hydraulic actuators, each valve section having a workport to which one of the plurality of hydraulic actuators connects, the pump being of the type which produces an output pressure that is a constant amount greater than a pressure at a control input, the array of valve sections being of the type in which the greatest pressure among the workports is sensed to provide a load sense pressure which is transmitted to the control input; the improvement within each valve section comprising: a pressure compensating valve that provides the load sense pressure at one side of a metering orifice which sees on the other side the output pressure of the pump so that the pressure drop across the metering orifice is substantially equal to the constant amount, the pressure compensator including: (a) a poppet slidably located in a bore thereby defining first and second chambers of the bore, the first chamber being in communication with the metering orifice and the second chamber being in communication with the control input of the pump wherein a pressure differential between the first and second chambers determines a position of the poppet with in the bore, the bore having an output port through which fluid is supplied to one of the hydraulic actuators, the poppet having a pilot passage between the first and second chambers; and   (c) a check valve within the pilot passage of the poppet and closing the pilot passage in response to pressure in the second chamber being greater than pressure in the first chamber.     
     
     
       14. The hydraulic system as recited in claim 13 further comprising a pressure relief valve to which the greatest pressure among the workports also is transmitted wherein the pressure at a control input is equal to the lower of (a) a set point pressure of the pressure relief valve and (b) the greatest workport pressure. 
     
     
       15. The hydraulic system as recited in claim 13 further comprising a spring located in the first chamber and biasing the poppet toward the first position.